The invention relates to catheters in general, and more particularly to improvements in catheters of the type employing an elongated flexible tubular member and means for deforming (particularly flexing) the distal end of the tubular member so that such distal end can be steered into selected passages in a human body or another animal body, e.g., into progressively narrower blood vessels.
It is well known to make an elongated flexible tubular member of a catheter from a suitable plastic material and to provide the tubular member with at least one longitudinally extending passageway or lumen. It is also known to make such tubular members of materials having different rigidities. The flexibility of the tubular member of a catheter depends upon its intended use. As a rule, the tubular members of presently known and utilized catheters can be classified as relatively stiff, highly flexible or reasonably or relatively flexible (i.e., neither stiff nor highly flexible). As a rule, the ability of a tubular member to resist torsional stresses is more satisfactory if its stiffness is high whereas a highly flexible member offers much less resistance to such stresses. At least some resistance to torsional stresses is often necessary because a suitably configurated and dimensioned distal end can be caused to change its orientation in response to turning of the proximal end of the tubular member about its longitudinal axis in order to properly position the tip of the distal end for advancement into a selected blood vessel or another passage in a patient's body.
In accordance with another known proposal, the introduction of the flexible tubular member of a catheter into a selected portion of a body passage is preceded by the introduction of an elongated wire or an analogous guide member which extends through and beyond the distal end of the tubular member. The latter is then advanced along the already introduced guide until its distal end reaches the selected portion of the passage. An advantage of such catheters is that they can utilize highly flexible tubular members.
The aforediscussed conventional catheters exhibit the drawback that their versatility is not entirely satisfactory. For example, it is often necessary to employ a catheter having a highly or at least reasonably flexible tubular member with a distal end whose orientation can be changed in response to rotation of the tubular body about its longitudinal axis and which is readily flexible so that its tip can enter any one of a number of relatively narrow passages in the body of a patient. Not only the orientation but also the inclination of the tip of the distal end of the tubular member should be changed by a person having access to the proximal end of the catheter. The tip of the tubular member of a catheter which exhibits the just discussed advantages can be manipulated to penetrate first into a relatively large blood vessel, thereupon into a narrower vessel and finally into a very narrow or very small blood vessel. Such catheters would exhibit the desirable characteristics as concerns their ability to penetrate into narrow or even extremely narrow body passages, e.g., to scan an internal organ (such as a human heart), to make endoscopic images of internal organs with assistance from light conductors, to subject internal organs to a treatment with one or more laser beams and/or for other purposes. Furthermore, one or more lumina of a properly inserted tubular member can serve for convenient and rapid introduction of various instruments (such as, for example, biopsy tongs) as well as for introduction of flowable pharmaceutic products, medications and/or others. Moreover, certain treatments can involve the introduction of probes which carry electrodes, e.g., in order to determine the electrical potential at the heart of a patient or to perform a high-frequency ablation. Still further, one or more lumina of a properly inserted tubular member forming part of a catheter can be utilized to permit convenient evacuation of liquids, contaminants and/or other flowable substances as well as to permit the introduction of diagnostic, surgical and/or therapeutic instruments.
German Pat. No. 39 20 707 A1 discloses a catheter with an elongated flexible tubular member having a distal end whose curvature can be altered by an eccentrically mounted pull wire. The tubular member of the patented catheter is provided with an external reinforcement or bead having a longitudinally extending passage for the pull wire. The distal end of the pull wire extends from the passage of the bead and is connected to the tip of the distal end of the tubular member so that the inclination of the distal end of the tubular member can be altered in response to the application of a pull to the proximal end of the wire. A drawback of the patented catheter is that the exposed portion of the pull wire between the distal end of the passage in the bead and the tip of the distal end of the tubular member is likely to damage the tissue in the body of a patient, e.g., in a human heart and particularly in a ventricle of the heart. Thus, a heart valve (such as a mitral valve) is likely to be damaged by the exposed portion of the pull wire if the distal end of the tubular member forming part of the patented catheter is to advance through the septum and into the the left atrium, thence through the mitral valve and into the left ventricle of a patient.
Another drawback of the patented catheter is that the provision of a tubular bead at the exterior of the tubular member of the catheter contributes to the cost and reduces the flexibility of a large part of the tubular member. At the very least, the external bead causes the tubular member to exihibit different flexibilities in different directions. Furthermore, if the tubular member is or should be quite flexible, the exertion of a pull upon the proximal end of the wire is likely to cause undesirable flexing of the entire tubular member rather than a desired flexing of the distal end of the tubular member. Thus, there exists an urgent need for catheters whose distal ends can be readily introduced into selected passages of a patient's body without causing irritation, damage or undesirable flexing.